April 13, 2017

SEX ON THURSDAY | Penile Plethysmography & You

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“Involuntary measures of sexual attraction and orientation.” That was the line that caught my eye on the website for the Cornell Sex and Gender Lab. The idea, as I understand it, is to hook a person up to electrodes, eye trackers and other sundry apparatuses. Then you show them softcore porn and measure how turned on they get. Intrigued, I emailed the director of the lab, hoping to be hooked up to these devices and experience the process firsthand. Within a few hours, though, he politely responded saying that he had retired and closed the lab. Not one to be easily discouraged, I continued reading about the subject online. I present here a summary of what I learned.

There are various physiological changes you can monitor — sweatiness (by passing a small current through the skin and measuring its conductivity) and eye dilation (by placing a camera in front of the pupil) are two of the tamer ones. My favorite measure of sexual arousal, though, is also the most obvious: erection.

It is a stereotype of male arousal that it tends to go one way or the other. That is to say, you’re either turned on or you’re not. While such platitudes are mostly true, they do overlook the realm of partial tumescence, the delightful stage in-between full erection and full flaccidity. Ask any man and he’ll tell you, upon a moment’s introspection, that his degree of tumescence is more or less a good indicator of his degree of arousal. Enter the penile plethysmograph, the tool of choice for phallometry. Phallometry is the process of measuring erections over time, and it may take any of several forms.

One type measures the volume of the penis directly, by using an inflatable cuff much like the cuff the doctor puts on your arm when he takes your blood pressure. The major difference is that this cuff goes on your penis. Another variety measures the girth. The device itself is a ring of rubber tubing which is fit snugly around the penis. The tube contains a small amount of mercury, and a computer logs the electrical resistance of the mercury column throughout the duration of the experiment. As the penis engorges, the column becomes thinner, changing its electrical resistance. To be precise, the resistance of a wire is proportional to its length divided by its cross-sectional area. Assuming a constant volume of mercury, it’s not too hard to show that the resistance is proportional to the circumference of the penis squared. Thus, we can take the square root of the resistance measurement, and record the man’s sexual arousal in units of ohm^1/2.

As if all this wasn’t interesting enough on its technological merits, penile plethysmography has strong political implications. Specifically, it is used on convicted sex offenders to judge their likelihood of reoffending. So, for example, the legal system may sit a prisoner down, attach a cuff to his penis, and force him to view imagery of children or of violence. Very Clockwork Orange, very 1984. According to a few sources, phallometry was invented by the Czech government to weed out draft-dodgers who claimed they were gay so they wouldn’t have to enlist. It’s very simple — show them erotic pictures of men and see if anything stirs down there. If not, off to war they go.

Of course, phallometry has perfectly acceptable uses in academia. It can quantitatively measure differences on the spectrum of human sexual orientation, as at Cornell, for example. But I think phallometry could be a big hit as a consumer product for long-distance couples. Imagine it — phone sex, plus an app to tell you in real time how your man is doing on the other end. Apple, you can have that idea for free. We’ll be waiting.


Dwight D. Eisenplower is a student at Cornell University. Bi Monthly runs alternating Thursdays this semester. Comments may be sent to [email protected]